It should be noted that recently it has become necessary to develop assemblies operating under low water pressures. Of these assemblies, capsule ones are the most efficient. These are the assemblies wherein a rotor, a turbine, and all auxiliary units are housed in a single shell or capsule. Since the sizes of a generator in such assemblies are considerably less than those of conventional hydraulic turbines, its normal operation requires a substantial increase in cooling intensity.
At present, in that field of engineering a great number of arrangements for cooling an excitation winding and rotor pole cores is known.
For example, known in the art are arrangements for rotor air cooling, comprising a powerful fan with an electric motor on the same shaft, mounted inside the head portion of the capsule. Such an arrangement thereof along with other auxiliary units tends to be rather complicated in design.
Some manufacturers practice cooling of capsule generators by compressed air.
The disadvantage of such a cooling system consists in that it requires sealing of the entry into the capsule as well as designing turbine and bearing seals so that the compressed air pressure would not force out the air into the used air stream through turbine seals and would not squeeze oil out from bearing reservoirs. The aforementioned requirements are also rather difficult to be obtained when designing the arrangement.
However, cooling with compressed air complicates seriously generator maintenance. Thus, to allow the personnel to enter the capsule to inspect or repair turbine or generator units contained therein, it is necessary that the pressure inside the capsule should be released and the fan stopped, this being allowable only for a short period of time in the course of assembly operation. A more prolonged stay of the personnel inside the capsule leads to forced stops of the assembly, which results in considerable degradation of its operating conditions.
It is known to use water cooling for stators and rotors of generators of capsule assemblies.
Water has a higher thermal capacity as compared to air and its heat transfer capability is many times over that of air.
Therefore, circulating along hollow conductors of stator and rotor windings, water provides very efficient heat removal.
Known in the art are arrangements for supplying water and oil in the system of a hydraulic turbine assembly, comprising two concentric pipes and a water header directly adjoining the generator shaft end with a distribution bush fixed thereupon. Water is supplied through the bush to the shaft bore connected with rotor windings of the generator. A water header comprises a pressure, a collecting and a drain chambers formed by interconnected stationary circular partitions. To separate the pressure chamber from the collecting and drain chambers, the casing of the water header is provided with circular and end seals sealing end clearances between the body and the rotatable bush.
The principal disadvantage of these arrangements consists in that they fail to provide self-adjustment of pressing the seals to the clearance forming members and, as a result, the arrangements have a low reliability. The absence of the water in the water header chambers even for a short period of time therefore results in a quick overheating and breaking of seals, the remains of broken seals may clog the hollow conductors of rotor windings, which, in turn, results in breakdown of the assembly.
Also known in the art is an arrangement for supplying cooling liquid into the rotor of an electric machine (cf. U.S. Pat. No. 3,335,303). The arrangement comprises two coaxial pipe members mounted on the rotor shaft, said pipe members forming a rotary part of the arrangement. The outer pipe member in the form of a bush is embraced by a pressure, a collecting, and a drain circular chambers formed by interconnected radial circular partitions. The radial partitions are mounted stationary and have a small radial clearance relative to the outer pipe member, eliminating a contact of stationary and rotary parts. The body is coupled with the rotary pipe members by means of antifriction bearings and rings.
Two coaxial pipes are required to provide thermal insulation between the cold liquid flow delivered from the pressure chamber to the inner pipe, and the hot flow contained in the collecting and drain chambers.
However, when using such arrangement for liquid supply into the rotor of an electric machine, there occur rather significant leakages of water from one chamber into the other through radial clearances between stationary circular partitions and the rotary pipe member. These leakages bypass the generator rotor and penetrate directly from the pressure circular chamber into the collecting chamber and may account to more than 50 percent of the total coolant liquid flow.
To compensate for increased water leakages and to ensure the sufficient cooling liquid flow, the pumps of increased capacity are required.
Furthermore, the cold water of leakages mixes in the collecting chamber with the hot water flowing from the rotor, decreases overall temperature of water in the collecting pipeline whereon temperature indicating instruments are installed, and thus distorts measurements of thermal state of the rotor.
Sufficient decrease in the amount of leakage is impracticable due to the fact that the clearances in the referred construction cannot be formed infinitely small, since the clearance dimensions are not stable due to temperature strains of the seal material of the stationary radial partitions.
Another disadvantage of this arrangement is the difficulty of its assembling, since when the two pipe members are mounted coaxially it appears to be difficult to mount seals in rather inaccessible spots inside the shaft.